Coaxial cable and method of making the same

Abstract

The present invention provides a small-diameter coaxial cable in which the same electrical and mechanical characteristics as in the prior art can be maintained and costs do not increase. The coaxial cable comprises a central conductor including three twisted wires and having a cross-sectional area of 0.005 mm 2 or less, a fluororesin insulation for covering the central conductor, an outer conductor disposed on the external periphery of the insulation, and a jacket for covering the outer conductor. The adhesive force between the central conductor and the insulation is one third or less the tensile strength of the central conductor. The method for manufacturing the coaxial cable comprises twisting three wires together to form a central conductor having a cross-sectional area of 0.005 mm 2 or less, extruding a fluororesin and forming an insulation on the central conductor so that adhesive force with the central conductor is one third or less the tensile strength of the central conductor, and providing the insulation with an outer conductor and a jacket.

The invention claimed is: 
     
       1. A coaxial cable comprising:
 a central conductor consisting of three single element twisted wires, the central conductor having an outer diameter and the three single element twisted wires having a twist pitch that is between 11 and 16 times the outer diameter of the central conductor, the central conductor having a cross-sectional area ≦0.005 mm 2 ; 
 a fluororesin insulation extruded on and covering the central conductor such that all of the twisted single element wires of the central conductor contact the fluororesin insulation as observed in a plane perpendicular to the longitudinal direction of the cable, the fluororesin insulation being a non-foam insulation material and voids being provided between portions of the central conductor and an inner surface of the fluororesin insulation; 
 an outer conductor disposed on the external periphery of the insulation; and 
 a jacket for covering the outer conductor; wherein 
 the adhesive force between the central conductor and the insulation and a breaking strength of the central conductor have the following relationship:
 adhesive force ≦⅓ breaking strength. 
 
 
     
     
       2. The coaxial cable according to  claim 1 , wherein the central conductor is a silver-copper alloy having a silver content of between 0.5 and 2.2 wt %.